Various types of methods and devices have been developed concerning fixing process of electrophotographic-type image forming apparatus. The most common method thereof is a pressurized heating method employing a heat roller.
In a fixing device in a pressurized heating method with the use of a heating roller (fixing roller), the fixing roller in which a material (mostly, fluorocarbon resin) having release characteristics from toner is formed on a surface thereof is applied, and, fixing is carried out as a result of a toner image side of a to-be-heated member (a recording material such as recording paper, OHP sheet, postcard or such) being made to contact the surface of the fixing roller under a pressure, and being made to pass therethrough.
In such a fixing device, one in which a heat efficiency of an outermost layer of the fixing roller which needs release characteristics from toner is improved is known. For example, Patent Document 1 proposes configuring a surface of a fixing roller by a nickel film in which fluorocarbon resin particles are mixed, and thus, improving thermal conductivity. Patent Document 2 proposes improving thermal conductivity by including carbon fiber in fluorocarbon resin in a surface of a fixing roller. Patent Document 3 proposes a heating roller and a fixing device in which thermal conductivity is improved with the use of crystallized graphite sheet. Patent Document 4 proposes, not a fixing roller, but a configuration in which, for the purpose of producing high temperature conducive complex, filler is dispersed in matrix resin, and the filler is melted and mutually continuously bonded via a metal mesh made of a metal having a low melting point of not more than 500° C. or an eutectic metal. Patent document 5 proposes producing an electrically conductive sheet by causing thermal conductive powder to contact magnetic material. Further, Patent Document 6 describes, as for electromagnetic induction heating, a thin electrically conducive layer made of SUS403 having magnetism with a thickness of 0.3 mm, with a thin fluorine coating on a surface as a surface heating layer. However, ordinarily, a fluorine coating on the order of 20 through 30 μm is required for maintaining release characteristics and durability, and this may degrade thermal conductive efficiency. Patent Document 7 discloses that a lubricative heating layer functions as an electromagnetic induction heating layer, and also, this has a function of improving lubricity of inner surface of a cylindrical fixing film as a heating member. Patent Document 8 discloses to provide a heating roller and a roller heating device superior in safety, by preventing electronic leakage due to contact of a coil with a roller member.
Patent Document 9 proposes blending metal powder having a melting point less than a burning temperature of fluorocarbon resin and more than a roller operation temperature in the fluorocarbon resin in a volume ratio of 0.5 through 40%, so as to provide non-electrification characteristic thereto (not for improving thermal conductivity). Patent Document 10 proposes to provide resin coating in which metal powder is included in a dispersed manner as a roller surface layer. Patent Document 11 proposes to add and disperse three-dimensional tetrapod-like electrically conductive whisker, whereby, thanks to the whisker, a roller surface and a roller shaft of each roller are electrically conducive with one another, so that electricity on the roller surface is effectively removed (implement of thermal conductivity being mentioned in an embodiment). Patent Document 12 discloses that a resin layer includes flake-like metal in a fixing roller having a coating of the non-adhesive releasable resin layer.
According to Patent Document 13, a proper voltage of a fixing member is maintained as a result of carbon black being included in a primer layer between a releasable layer and a core metal, or a bias voltage is applied to a fixing roller, toner's electrostatic adhesion is avoided and image turbulence due to charged roller is avoided. Patent Document 14 relates to an intermediate transfer body, in which varistor powder is dispersed in a belt. Patent Document 15 discloses a configuration in which an electrically conductive mylar is bonded to a transfer paper facing surface of an entrance guide, and thereon, an isolative mylar as a non-electrically conductive sheet part is bonded. Further, a configuration is disclosed in which as a device for applying bias to the electrically conductive part, a configuration is provided to apply a constant voltage of +2 [KV] from a power source. Thereby, toner dust generation on the entire surface of a transfer paper which otherwise may occur due to approach or contact of the transfer paper to the entrance guide can be avoided.
Patent Document 16 discloses an induction heating body manufacturing method characterized in that a complex is produced from a metal porous body having passing through holes with polymer or ceramics which is impregnated, filled with or laminated, or a combination of a plurality thereof.
However, in the invention described in Patent Document 1, since merely fluorocarbon particles are mixed into a nickel layer, releasability of a fixing roller surface may not be sufficient, and offset may occur so that an image may be stained. Further, in a heating method with the use of electromagnetic induction, eddy current is required to flow, and thus, sufficient heating may not be expected in an electric conductor separated by an insulator. As a result, it is not possible to apply it for achieving an object of the present invention. In the invention described in Patent Document 2, it is described that too much mixing of carbon fiber may obstruct releasability, and improvement of thermal conductivity is limited. In the invention described in Patent Document 3, a releasable layer is required on a crystallized graphite sheet for the purpose of ensuring releasability. Thus, improvement in thermal conductivity is limited. In the invention described in Patent Document 4, since merely high temperature conductive complex is produced, releasability from toner which is most important factor of a fixing roller is not provided, and thus, toner easily adheres thereto. Thus, it is not possible to apply it to a fixing roller. In a method such the invention described in Patent Document 5 in which magnetism is utilized, magnetic particles easily agglutinate near to a magnetic field generating source. As a result, magnetic particles having insufficient releasability gather on a surface which needs releasability when this method is applied to a releasable layer, and thus, it is not possible to ensure releasability. Thus, it is not possible to apply it to a fixing roller. In the invention described in Patent Document 6, a fluorine coating layer on the order of 20 through 30 μm is required for keeping durability, which may degrade thermal conductive efficiency, and thus, the performance approaches that of an ordinary halogen lamp. In the invention described in Patent Document 7, thermal conductive efficiency is not sufficient since a heat generation layer is provided inside, heat supply may not be made sufficiently, and thus, a time is required for increasing the temperature of the outermost surface upon starting up.
In the configuration of Patent Document 9, a volume ratio of metal required for improving thermal conductivity is larger than a volume ratio required for non-electrification characteristic. Further, melted metal does not easily cause fluorocarbon resin to get wet therewith, metal agglutinates when the metal is added in a volume ratio necessary to improve the thermal conductivity. Then, after it is cooled, metal particles each having a large diameter result therefrom. Thereby, such metal particles having large particle diameters are exposed, toner easily adhere thereto, and thus, offset may occur. In the configuration of Patent Document 10, since an adiabatic zone of fluorocarbon resin exists even with simple addition of metal powder, it is necessary to increase a blending amount to obtain sufficient thermal conductivity. Thereby, releasability is lost. Thus, offset may occur. In the configuration of Patent Document 11, since an adiabatic zone of fluorocarbon resin exists among whiskers even with simple addition thereof, it is necessary to increase a blending amount to obtain sufficient thermal conductivity. Thereby, releasability is lost. Thus, offset may occur. In the configuration of Patent Document 12, since an adiabatic zone of fluorocarbon resin exists even with simple addition of metal flakes, it is necessary to increase a blending amount to obtain sufficient thermal conductivity. Thereby, releasability is lost. Thus, offset may occur.
In the configuration of Patent Document 13, a part having high resistance remains on an outermost surface. Thereby, a part having a high charged voltage remains, wherewith toner dust may occur. In the configuration of Patent Document 14, an idea of carrying out electric potential control with the use of varistor powder is the same. However, it is not necessary to consider softened toner's releasability, different from a fixing member, and it is possible to achieve the object by dispersing a sufficient amount of varistor powder. Therefore, when applying the same configuration to a fixing member, softened toner's adhesion occurs, and thus, it is not possible to apply. In contrast thereto, according to the present invention, it is directed to controlling electronic potential by minimizing inorganic powder part exposed on the surface. In the configuration of Patent Document 15, the same as the configuration of Patent Document 13, it is difficult to avoid partial generation of toner dusts
In the configuration of Patent Document 16, a metal porous body having passing through holes are produced previously, and resin or such is impregnated in gaps thereof. Therefore, it is difficult to produce a uniform configuration with the use of resin (which is not easily impregnated since it has a high viscosity) having a high melting point on a roller or on a belt.
Patent Document 1: Japanese Laid-open Utility-Model Application No. 1-164463;
Patent Document 2: Japanese Laid-open Patent Application No. 6-43776;
Patent Document 3: Japanese Laid-open Patent Application No. 2001-117402;
Patent Document 4: Japanese Laid-open Patent Application No. 6-196884;
Patent Document 5: Japanese Laid-open Patent Application No. 2001-267480;
Patent Document 6: Japanese Laid-open Patent Application No. 2001-5315;
Patent Document 7: Japanese Laid-open Patent Application No. 2001-6868;
Patent Document 8: Japanese Laid-open Patent Application No. 10-153918;
Patent Document 9: Japanese Patent Publication No. 07-036097;
Patent Document 10: Japanese Laid-open Patent Application No. 02-047671;
Patent Document 11: Japanese Laid-open Patent Application No. 2002-91217;
Patent Document 12: Japanese Laid-open Patent Application No. 04-067187;
Patent Document 13: Japanese Laid-open Patent Application No. 7-325498;
Patent Document 14: Japanese Laid-open Patent Application No. 2002-229346;
Patent Document 15: Japanese Laid-open Patent Application No. 2004-145021;
Patent Document 16: Japanese Laid-open Patent Application No. 10-165311; and
Non-Patent Document 1: Written by Nobuo Saito, ‘Actual Technology for Electrically Conductive Resin’, CMC Co., Ltd., p. 64 (2000).